Many oncogenes act by disrupting pathways regulated by peptide growth factors. These oncogenes transform cells by causing inappropriate production of growth factors or by encoding mutated growth factor receptors. These mechanisms for transformation will be investigated using two different experimental systems. The neu oncogene will be studied to determine the mechanism of activation of an oncogenic growth factor receptor. A model autocrine system, in which cells are transformed because they constitutively produce EGF, will be used to develop methods for reverting transformation mediated by autocrine circuits and to identify genes that cooperate with the EGF gene in cell transformation. The neu oncogene encodes a protein designated p185 that is closely related to, but distinct from, the receptor for EGF. The product of the neu proto-oncogene is itself likely to be a growth factor receptor. Because normal and transforming forms of p185 differ by only a single amino acid replacement, this system is ideal for investigating the mechanism of oncogenic activation of a growth factor receptor. The effects of the activating mutation on activity and specificity of the p185 kinase, sites of phosphorylation of p185, and oligomerization will be examined. These studies will yield insights into the mechanism of signal transduction by the tyrosine kinase family of growth factor receptors. Cells expressing a transfected EGF gene at high levels are tumorigenic but differ from ras-transformed cells in being anchorage-dependent and growing only slowly as tumors. These partially transformed cells will be used to study multi-step carcinogenesis in which one of the affected genes induces production of EGF-like factors. Genes that are known to act synergistically with EGF in stimulating cell proliferation will be tested for the ability to cooperate with EGF in tumorigenesis. Transformation by the EGF expression plasmid is mediated by an extracellular autocrine circuit that can be interrupted with an anti-EGF monoclonal antibody. EGF-transformed cells will be used as a model therapeutic system for tumors mediated by autocrine circuits. These cells will be used to test the efficacy of anti-EGF antibodies, anti-EGF receptor antibodies, and EGF antagonists in blocking tumorigenicity.